Currently, there are a number of systems known utilizing a variable rate moving sprinkler head directing one or more streams away from the sprinkler outlets or nozzles. For instance, a common type of yard sprinkler is referred to as an oscillating wave lawn sprinkler and includes a generally horizontally oriented and upwardly curved tube with a plurality of holes or nozzles along a top portion of the tube for discharging water. When the sprinkler is activated, the tube is rotated in an oscillating manner while the water is emitted in a wave-like pattern. As the tube is rotated, the emitted water streams from the nozzles moves over a pattern of ground to either side of the sprinkler. The tube element is rotated in a first direction, slows as it reaches a limit, pauses at the limit, and then is counter-rotated in a second direction opposite the first direction. In this manner, this type of sprinkler is referred to as a reversing sprinkler and, hence, a variable rate or velocity sprinkler.
Such a form of intermittent sprinkler utilizes an irregularly-shaped cam member. The rotating cam member is typically heart-shaped, for instance, so as to have a rounded portion forming two lobes divided by a cleft. An engagement member of the drive mechanism rides against the rotating cam member so that a first angular velocity, generally constant, is produced when the engagement member follows the rounded portion of the heart-shaped cam member, and so that the angular velocity approaches zero when the engagement member approaches the cleft. The sprinkler reverses once it passes beyond the cleft. Accordingly, the sprinkler pauses at the same areas at the limit of the sprinkler travel, and the design suffers from over-watering of these areas without reducing the tailing effect throughout the cycle.
With the above-described oscillating or reversing sprinkler, a greatest throw distance is only achieved at the limits of the movement. A greater amount of water is deposited at these limits, in part due to the fact that the sprinkler slows, stops, and reverses, therefore spending a disproportionate time watering an area reached by the greatest throw distance and the area adjacent thereto until the sprinkler reaches its normal rate of movement.
A stationary sprinkler will produce the maximum emission or throw distance for a water stream emitted therefrom. That is, the throw distance is based on a number of variables, including the rate of rotation. If the sprinkler is stationary and the rate of rotation is zero, the throw distance is based on the characteristics of a flow path through the sprinkler, and water pressure, among others. Assuming all these variables are held constant, other than rate of rotation, the stationary sprinkler produces the greatest throw distance. To be more precise, the water stream develops a profile when emitted, and the distance any particular droplet of water is thrown is related to the exit velocity at the nozzle, to force from subsequent droplets following the same path, and to cohesive forces between water droplets. With a stationary sprinkler, each droplet of a water stream is being driven by each successive water droplet, and each preceding water droplet reduces the air resistance experienced by the subsequent droplet.
When the sprinkler is rotating, each water droplet is emitted at a position somewhat offset from the preceding and succeeding droplets. Accordingly, a first water droplet does not receive as great a push from a subsequent water droplet, nor does it benefit from reduced air resistance. The faster the rotational velocity, the greater the offset between adjacent water droplets, the less each droplet is able to assist the throw distance of the other droplets. Accordingly, this interaction causes a “tailing” effect, and the faster the rotational velocity is, the greater the tailing effect. The result is that the water stream profile is not able to sufficiently develop for a desirable throw distance, and a tailing water stream is discharged an undesirable distance from the moving sprinkler head.
Rotating sprinklers have been employed to make the distribution from a moving sprinkler more even. A rotating sprinkler utilizes one or more nozzles discharging water in a generally radially direction, preferably above horizontal, to throw water a distance from the sprinkler to cover an area therearound. With the above-discussed oscillating sprinkler, the water streams repeatedly discharge water to the greatest distance at the limit of the oscillation, and the area between the greatest distance is watered during the counter-rotation by the sprinkler. With a rotating sprinkler, the water stream is generally emitted a particular throw distance and would not ordinarily provide significant water to the area short of this throw distance.
Various designs have been created for providing water at a varying water distances. For instance, the sprinkler may have a plurality of nozzles emitting water at various trajectories or pressures. Alternatively, the nozzle geometry may be structured to distribute water in a pattern other than a stream.
Other sprinkler designs have utilized an intermittent motion to produce a varying rotational rate. A typical rotating sprinkler utilizes a drive mechanism that generally converts force from the water flow through the sprinkler into high velocity rotation in a turbine, for instance. The turbine is then mounted on an axle for driving a gear reduction mechanism for reducing the velocity into high torque. The drive mechanism then cooperates to rotate a portion of the sprinkler.
An example of a rotating sprinkler having an intermittent motion is U.S. Pat. No. 5,758,827, to Van Le et al., which utilizes cooperating gears of the gear reduction mechanism with an irregular gear tooth pattern. For instance, one embodiment has a first gear with a single tooth such that the tooth engages with a second gear for a short period, and then disengages for a longer period of time. During the time the single tooth is disengaged, the second gear is generally stationary, and the water stream profile is allowed to more fully develop. The single tooth first gear then re-engages to effect a short motion of the second gear, whereupon the first gear disengages.
It should be noted that such an intermittent sprinkler generally has two speeds, namely moving and stationary. That is, the sprinkler rotates at a particular speed when engaged, save for inertial effects, and then does not rotate when disengaged. In addition, there is an impulse force transmitted through the sprinkler and its mechanisms, as well as to the water flow, that causes stresses and pressure fluctuations as the turbine and gear mechanism is disengaged and re-engaged. Furthermore, the sprinkler tends to spend a period of time delivering water to a particular area, then is quickly rotated to deliver water to a subsequent area. Consequently, the sprinkler tends to localize the distribution of water in areas. This is exacerbated by the fact that such a sprinkler often waters the exact same locations on each full rotation.
Accordingly, there has been a need for an improved rotating sprinkler having a varying rate or velocity that provides improved water distribution.